Wired radio broadcasting system



INVENTOR MAD/O Filed Sept. 5, 1923 R. D. DUNCAN, JR

is? MF WIRED RADIO BROADCASTING SYSTEM March 22 1927.

ATTORNEY Patented Mar. 22, 1927.

UNITED STATES PATENT OFFICE.

ROBERT 1). Duncan, JR, or BRONXVILLE, NEW- YORK, ASSIGNO-R r WIRED immo,

INC., 015 NEW YORK, N. Y., A CORPORATION OF DELAWARE.

WIRED RADIO BROADCASTING sYsrnM.

Application filed September 5, 1923. Serial No. 661,037.

This invention has to do with communication systems, and relates, more particularly, to systems for broadcasting intelligence over wide areas to large numbers of listeners simultaneously.

Prior to the present invention, it was known that telephonic messages could be transmitted overwmetallic transmission lines, such as a telephone line, throughthe medium of so-called carrier currents of super-audible high frequency modulated in accordance with the signals to be transmitted, but in so 'a plurality far as it has been possible to ascertain, it was not known that use of carrier currents for broadcasting to many subscribers over polyphase transmission lines within the community or cit where the wires are simultaneously use p for other purposes, suchas the transmission of electric power and lighting current could be successfully effected. The present' invention, therefore, is directed to the provision of an operable system for broadcasting through the medium of carrier currents oyer electric power transmission lines, and, more specifically, over alternating current transinission lines, as, foi' instance, the power and lighting networks of cities. a

In addition to the broad idea hereinbefore stated, the present invention lies, in part, in the discovery of a workable and practical system, characterized by the utmost simplicity whereby high frequency signaling carrier currents can be impressed on multi-phase transmission lines for transmission thereover and received with perfect clarity from any single-phase branch of the multi-phase system.

The usual practice in alternating current power transmission over a city is to conduct the high-voltage power from the main power house'over three-phase transmission lines to of substations where the high voltage is stepped down. The three-phase lower voltage output of the substations is then usually branched out into a plurality of single-phase branches which, in turn, are branched oil through step-down transformers to the individual consumers.

Prior to the carrying out of experiments which resulted in the above-noted discovery, it was thought'thatin order to broadcast over combined multi-phase' and single-phase systems and, particularly, combined threephase-three-wire and single-phase-two-wire is to say, from anyof the branches of the three-phase system.

A clearer understandingof the invention may be had from the following detailed description in conjunction with the accompanying drawing.

The drawing shows a diagrammatic illustration of an alternating current power distribution system comprising a central station' 1. and two substations 2 and 3.

' At thecentral station 1 there is shown a three-phase A. O. generator 4, Y-connected for example, a switchboard 5 and bus bars 6, 7 and 8, from which the various outgoing branches extend to the substations 2, 3, etc.

At each of the substations there is shown a three-phase step-down transformer 9, 9 together with bus bars 10,11, 12, 10 11, 1,2 and switch boards 13, 13* containing the customary power apparatus.

Extending from each of the substations 2 and 3. there are shown three single-phasetwo-wire transmission lines comprising conductors 14, 15, 16, 17, 18, 19,14 15, 16 17 18, 19. Conductors 14 and 15 are connected to bus bars 11 and 12 while conductors 16 and 17 .are connected to bus bars 10 and 12 respectively, and conductors 18 and 19 are connected to bus bars 10 and 11 respectively. Each of these outgoing branches is', therefore, fed by a difi'erent phase of the three-phase system. The same is true with respect to the outgoing lines from substation 3. A

Bridged across each of the outgoing lines there may be one or more step-down transformers such as transformer 20 for stepping down the voltage to the usual service volt age, that is, 110 volts. Reference characters 21, 22 represent conductors'extending to a customers house or other building wherein are shown electric lights 23. The other cusrespectively tomer installations shown are similar to that just described and will be clearly understood from the drawing. Associated with central station 1 there i shown a broadcasting studio 24, in which is installed apparatus for generating and modulating high frequency carirer currents in accordance with music, speeches .and the like, which is to be broadcast over the power transmission lines. This installation includes a high frequency generator 25, a modulator 26, and microphone 27 similar to the usual radio transmitter.v mitter is connected through conductors 28 and condensers 29, 30 to conductors 31, 32 of the three-wire transmission system. It will be noted that the high frequency transmitter is not directly connected to the third conductor 33 f the three-wire system.

Each of the customers installations illustrated' includes apparatus 34 for receiving and detecting the modulated high frequency carrier current and, a loud speaking telephone 35. The receiving apparatus is connected across the power or lighting lines, but

- in order to prevent low frequency currents .reaching the receiving apparatus, one or more blocking condensers 36 are preferably inserted in the connection between the lines and the receiver. These condensers do not materially impede the passage of high frequency carrier currents, but they effectively prevent the passage of the more'dangerous low frequency current.

By tracing the circuit connections from the central station to the various customer installations, it will be seen that certain of them are so associated with the three-phase distribution system that the high frequency carrier currents would, seemingly, not be impressed ontheir branch lines. This is the case with the installation fed from transformer 20. The fact is, however, that the carrier current finds its way to all of the branch circuits and may be received from any of them, there being no apparent differ-- ence noted in the volumeof s'ound obtainable from the different branches.

N0 completely satisfactory explanation of this unexpected phenomenon can be given but this is not essential to a complete an operative disclosure of the invention such as will enable those skilled in the art to practice the invention.

. I claim:

1. A signaling system comprisingamultiphase electric generator, a multi-phase power This transtransmitter being connected to less than the total number of said conductors, whereby high frequency carrier currents are directly impressed on 'at least one but less than the total number of conductors comprising the multi-phase power transmission line, high frequency signal receiving devices and means connecting them to a plurality of said branch lines, the arrangement being such that the high frequency carrier current is receivable on a plurality of said branch lines including branch lines whose phases do not correspond with the conductors of the multiphase transmission line with which said transmitter is connected.

2. A wired radio broadcasting system comprising in combination a polyphase electric power distribution system including a plurality of line conductors for conveying power to a plurality of subscriber stations, a source of high frequency current, means for modulating 'said source, connections between said high frequency source and at least twp of said line conductors, high frequency signal receiving circuits located at said subscriber stations and having connections to said line conductors differing from the line conductors to which said high fresource may be connected. wired radio broadcasting system comprising in combination a polyphase electric power distribution-system including a plurality of conductors for polyphase current, a plurality of branch circuits extending from said conductors, a plurality of subscriber circuits connected with said branch circuits, a high frequency signal transmitting system connected to not more than one phase of said polyphase distribution system, and high frequency signal receiving circuits connected with said subscriber circuits and to all of the phases of said polyphase distribution system for receiving high frequency signaling current impressed by said transmitting system upon one of the phases of said polyphase electric power distribution system.

- In testimony whereof I aflix my signature.

RoBERT n. DUNCAN, JR. 

